[R] Dichotomous variables

[Sarah Goslee]

Hi Marco,

On Fri, Aug 5, 2011 at 11:53 AM, marco <marco.milella at aim.uzh.ch> wrote:
> Hi everyone,
> Have sample of items for each one, a set of 20 dichotomous (absent-present)
> variables are expressed. I'm trying to understand how to explore the
> co-occurence of each variable.
> Read some papers concerning smallest space analysis, but it does not seems
> implemented in any R package (and my protamming skills are =0).
> Non metric MDS gives error messages, probably because of the dichotomous
> character of my variables.
> My aim is basically to obtain a 2D plot with cooccurence expressed as
> distance between plots (variables).
> Any advice to such issue?

I would think that NMDS with a dissimilarity metric appropriate for
presence-absence data is a reasonable place to start.

Since you don't give any details about your data, or the commands you
used to run NMDS, or even the error messages you received, we can't
help further.

You did calculate a dissimilarity before trying to run NMDS, right? Having
binary variables doesn't make a bit of difference.

Sarah

-- 
Sarah Goslee
http://www.functionaldiversity.org